Covalent Graphene Functionalization for the Modification of Its Physical Properties

Abstract: Graphene, a two dimensional monolayer carbon sheet with the atoms tightly packed in a hexagonal lattice, has exhibited so many excellent properties, which enable graphene to break several material records with regard to carrier mobility, strength yield and thermal conductivity to name a few. Therefore, graphene has been placed as a potential candidate to allow truly next-generation material. Graphene is a zero band gap material, implying that an energy band gap around the Dirac point is supposed to be open to make graphene applicable as a semiconductor. Covalent bond graphene functionalization becomes an essential enabler to open the energy gap in graphene and extend graphene applications in electronics, while the densely packed hexagonal carbon atoms as well as the strong sp2 hybridization carbon-carbon bonds jointly result in a changeling topic of allowing graphene to be decorated with functional groups.Here in this thesis, different routes to realize graphene functionalizations are implemented by using physical and chemical ways. The physical functionalization methods are the ion/electron beam induced graphene fluorination as well as local defect insertion and the chemical ways correspond to the photochemistry techniques to approach hydrogenation and hydroxypropylation of graphene. Furthermore, to incorporate graphene into devices, the tuning of mechanical properties of graphene is desired. Towards this aim, the structure modification of graphene is employed to investigate the nanometer size-effect of crystalline size of graphene on the mechanical properties, namely Young’s modulus and surface energy. In the process of the graphene hydrogenation project, we discovered a high yield way to synthesis high quality graphene nanoscroll (GNS). Interestingly, the GNS shows superadhesion property through our atomic force microscopy measurements. This superadhesion is around 6-order stronger than van der Waals interaction and even higher than the hydrogen bonding enhanced and solid/liquid interfaces.